A variety of strategies have been applied to identify specific genes which are sensitive to low-dose radiation (0.7 mGy/h), but gene expression at the protein level has not been confirmed. In contrast, the genes identified in the present invention are revealed by differences in gene expression at the RNA level as well as at the protein level. Also, no attempts have been made to compare the expression patterns of genes associated with DAN damage and repair between healthy mice and cancer-induced mice, both of which are subjected to low doses of radiation. Moreover, it has not previously been known that the genes identified in the present invention are responsive to low-dose radiation. Some conventional studies, as will be described below, have characterized gene expression profiles which are responsive to low doses of radiation.
i) A human myeloid leukemia cell line was irradiated to a dose between 2 and 50 cGy, and the induction of five genes, CDKN1A, GADD45A, MDM2, BTG2 and PHLDA3, was observed (Amundson et al, 2003).
ii) When human blood was irradiated at doses of 0.5, 2 and 8 Gy, radiation-sensitive genes, FDXR, CDKN1A, PHPT1, BBC3 and SESN1, were identified, which have the potential for use to assess the amount of radiation exposure in the event of a radiation accident (Paul and Amundson, 2008).
iii) After C57BL/6J mice were irradiated at a dose rate of 0.032 to 13 μGy/min for a period of 485 days, kidneys and testicles were collected and subjected to microarray analysis, which identified genes sensitive to low doses of radiation (Taki et al, 2009).
iv) After male C57BL/6J mice were irradiated to 8 Gy, 0.4 Gy or 0.02 Gy at a dose rate of 17-20 mGy/day or 0.86-1.0 mGy/day for a period of 401 to 485 days, livers were collected and assessed by microarray analysis and reverse transcription polymerase chain reaction (RT-PCR), resulting in the identification of genes sensitive to low-dose radiation (Uehara et al, 2010).
v) Microarray and quantitative polymerase chain reaction (qPCR) analysis revealed 39 genes sensitive to low-dose radiation in Drosophila melanogaster exposed to low-dose radiation (Seong et al, 2011).
vi) When human blood was irradiated to 0, 0.02, 0.1, 0.5, 1, 2 and 4 Gy, microarray analysis revealed a total of nine genes responding to low doses of radiation. Also, gene groups differentially expressed according to dose rates and post-irradiation times were selected so as to be used for bio-dosimetry assay (Knops et al, 2012).
vii) Zebra Danio embryos were irradiated with 0.1 or 1 Gy, and liver mRNA was used for microarray and quantitative PCR analysis, resulting in the identification of radiation-sensitive genes (Jaafar et al, 2013).
viii) Human blood was exposed to 5 to 500 mGy radiation and assessed by microarray analysis, thus identifying genes sensitive to low-dose radiation (Nosel et al, 2013).